🎨 Introduce contextualized logging

This commit is multi-fold as it also refactors internally context and logger
as interfaces so it is easier to plug luet as a library externally.

Introduces a garbage collector (related to #227) but doesn't handle yet
parallelism.

Closes #265

vendor/github.com/mattn/go-isatty/isatty_bsd.go

@@ -0,0 +1,19 @@
+//go:build (darwin || freebsd || openbsd || netbsd || dragonfly) && !appengine
+// +build darwin freebsd openbsd netbsd dragonfly
+// +build !appengine
+
+package isatty
+
+import "golang.org/x/sys/unix"
+
+// IsTerminal return true if the file descriptor is terminal.
+func IsTerminal(fd uintptr) bool {
+	_, err := unix.IoctlGetTermios(int(fd), unix.TIOCGETA)
+	return err == nil
+}
+
+// IsCygwinTerminal return true if the file descriptor is a cygwin or msys2
+// terminal. This is also always false on this environment.
+func IsCygwinTerminal(fd uintptr) bool {
+	return false
+}